1. Field of the Invention
This invention relates to an electrode forming process for forming an ohmic electrode on a compound semiconductor having a substrate of a p-type GaAs-based material.
2. Related Background Art
Conventionally as ohmic contacts on p-type GaAs and p-type Al.sub.x Ga.sub.1-x As, Ti/Pt/Au and Cr/Au electrode structures have been studied as the non-alloy type, and AuZn, AuMn, AuBe, Pt/Zn/Au and Pd/Zn/Pd/Au electrode structures have been studied as the alloy type. Specifically, for example, Japanese Patent Laid-Open Publication No. SHO59-189669 describes forming an ohmic contact by alloying of Pt and GaAs. Extended Abstract 5p-G-16 (The 49th Spring Meeting, October 1988); The Japan Society of Applied Physics and Related Societies) describes forming an ohmic contact being Pt/Zn ohmic contact.
Requirements of these electrodes are 1) exhibition of low resistances, 2) flat and smooth surfaces, 3) no diffusion of electrode materials into substrates, 4) long-lasting reliability, and others.
Generally the non-alloy ohmic contact satisfies the above-described requirements 2 to 4 but, in comparison with the alloy ohmic contact, does not exhibit sufficiently low contact resistance. However the alloy ohmic contact exhibits sufficiently low contact resistance owing to increased surface impurity concentrations due to diffusion of active p-type dopants contained in the electrode materials. Resultantly a sufficiently low contact resistance whose specific resistance is below 10.sup.-6 .OMEGA. cm.sup.2 can be obtained. However problems with the alloy ohmic contact are diffusion of impurities or electrode materials into the substrate, and low reliability and so on.